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    <title>Document</title>
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<body>

</body>
<script>
    var set = (name, cvalue, exdays) => {
        var d = new Date();
        d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
        var expires = "expires=" + d.toGMTString();
        document.cookie = name + "=" + cvalue + "; " + expires;
    }
    var fun = (name) => {
        var a = name + '='
        var b = document.cookie.split(';')
        for (i = 0; i < b.length; i++) {
            var c = b[i].trim()
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                return c.substring(a.length, c.length)
            }
            return ''
        }
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    // console.log(fun())
    check = () => {
        var user = fun("username");
        if (user != "") {
            alert("欢迎 " + user + " 再次访问");
        }
        else {
            user = prompt("请输入你的名字:", "");
            if (user != "" && user != null) {
                set("username", user, 30);
            }
        }
    }
    check()
</script>

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